we did the same thing to my friend freshman year of college on halloween after she killed a bottle of jose cuervo. when we asked her how she was taking all these "shots", all she said was how good she was at taking shots.. if she only knew then what she knows now! hahahaha

I swapped my drunken friend's vodka shots for water ones once. She noticed the difference, so I went "Okay fine have the vodka ones" and gave her back the water shots. Suddenly she didn't notice any difference. Hmm..